Analysis of Respiratory Signals in Spectral Domain for Detecting Respiratory Disorders with Emphasis on COVID-19

Sound signals from different processes of respiratory system are vital indicators of human health. With the onset of Coronavirus pandemic, the importance of early diagnosis of respiratory disorders has further been highlighted. In this paper, research works related to analysis of respiratory system functioning in spectral domain using acoustic signal processing methods has been reviewed with special focus on work related to COVID-19 diagnosis using non-invasive techniques. Various deep learning and machine learning models for identifying acoustic biomarkers of COVID-19 have been studied and summarised. Three modalities that have been considered are breathing, cough and voice recordings. Feature extraction techniques on these modalities have been reviewed for classification, prediction and similarity metrics analysis. Another vital health parameter is the rate of respiration that can be estimated by performing spectral analysis of sound signal envelope of breathe signal recording. Various datasets and pre-processing techniques related to sounds associated with symptoms of respiratory disorders including COVID-19 sounds have also been listed.